Draft gear assemblies which utilize friction-type clutch mechanisms to absorb heat energy generated during service have been in widespread use on railway cars for several years prior to the present invention, as is generally well known in the railway art. These draft gear assemblies are disposed within an elongated opening located in the center sill member of the railway car along the longitudinal axis thereof and behind the shank, or innermost end, of the railway car's coupling mechanism.
In this position, these friction clutch type draft gear assemblies will absorb at least a relatively large portion of both the buff and draft forces generated during service. Such buff and draft forces encountered by such railway car are usually being applied in an alternating manner to the center sill member during normal car operation on the track.
Many of such prior art type friction clutch draft gear assemblies are taught in U.S. Pat. Nos. 2,916,163; 3,178,036; 3,447,693; 4,645,187; and 5,152,409. Each of the above-identified patents is owned by the assignee of the present invention. The teachings of each of these patents are also all incorporated into the present application by reference thereto.
It is quite well recognized, by those persons who are skilled in the art of friction clutch type draft gear assembly design, that there are a number of significant reasons why lighter weight draft gear assemblies are desirable in the railroad industry. The first reason is that less energy is required to move the railway car over the track structure. A second reason is that additional pay load may be carried by such car without exceeding a load limit on a particular track structure and without incurring increased energy costs. A third reason is that railroads are continuously attempting to increase load carrying capacity of modern railway cars.
Nevertheless, regardless of the weight of such draft gear assembly, it must be capable of maintaining the minimum shock absorbing capacity during its service life. This minimum shock absorbing capacity is specified in the standards which have been established by the Association of American Railroads (AAR), particularly, AAR specification M-901G. This specification, for example, requires that these draft gear assemblies have a rated capacity of at least 36,000 foot pounds and a rated velocity of at least 5 MPH. Also, it is important to note that the shock absorption must be accomplished without exceeding a 500,000 pound peak reaction force applied to the coupler of the railway car.
However, even though a light weight design of the draft gear assembly taught in U.S. Pat. No. 5,152,409 has been successfully used in railway applications, it has not been found adequate to meet AAR-M-901G specification requirements.